1. Field of the Invention
The present invention relates generally to interlocking closure devices for thermoplastic storage bags, and more particularly, to an interlocking closure device which proceeds in more than one step when the closure device is being closed.
2. Description of the Related Art
The use of closure devices for fastening storage containers, including plastic bags, is generally known. Furthermore, the manufacture of closure devices made of plastic materials is generally known to those skilled the in the art, as demonstrated by the numerous patents in this area.
A particularly well-known use for closure devices is in connection with flexible storage containers, such as plastic bags. In some instances, the closure device and the associated container are formed from thermoplastic materials, and the closure device and the sidewalls of the container are integrally formed by extrusion as a single piece. Alternatively, the closure device and sidewall of the container may be formed as separate pieces and then connected by heat sealing or any other suitable connecting  process. In either event, such closure devices are particularly useful in providing closure means for retaining matter within the bag.
Conventional closure devices typically utilize a thermoplastic zipper in the form of mating fastening strips or closure elements, which are used to selectively seal the bag. The fastening strips comprise interlockable male and female profiles. With such closure devices, however, it is often difficult to determine whether the fastening strips are fully occluded. The problem addressed by the present invention pertains to the determination of closure or nonclosure of the zipper of a reclosable thermoplastic bag.
One technique for aiding in the determination of the state of zipper is to utilize a zipper that imparts a visual color change upon closure. Different colors may be utilized in each of the opposing zipper profiles to produce a third distinct color when interlocked. Zippers utilizing such a color change are seen in U.S. Pat. Nos. 4,186,786 and 4,285,105.
It is well understood that all thermoplastic zippers have an occlusion and peel force. For example, U.S. Pat. No. 5,368,394 to Scott et al. discloses a reclosable bag with closure profiles having stabilizer wedges. Using these stabilizer wedges, the force required to open the bag may be preselected by appropriately choosing the angles at which the surfaces of stabilizer wedges contact one another. It is also known that a desired tactile effect can be achieved during opening or closure of the zipper by changing the occlusion and peel force along the length of the zipper. In another example found in U.S. Pat. No. 7,137,736 to Pawloski et al., the reclosable pouch with a first closure mechanism having a first closure characteristic and a second closure mechanism having a second closure characteristic.
One technique for changing this force is to remove portions of one or both of the male and female zipper profiles such that there is a discontinuity in structure in those portions of the opposing profiles which contact each other upon interlockment of the zipper. Examples of zippers having closure profiles with portions removed are disclosed in U.S. Pat. No. 5,070,584 to Dais et al. and U.S. Pat. No. 5,647,100 to Porchia et al.
However, there still exists a need for alternative and improved thermoplastic closure members that impart a closure perceptible to the touch so that the fact of closure can be confirmed by a nonvisual means, i.e., by feel.
Accordingly, it is desired to provide a reclosable bag having an improved closure member that imparts a multistep process perceptible to the touch; and it is desired to provide a method for production of the reclosable bag wherein material is not removed from the closure region such that leak resistance through the closure is improved.